The present invention is directed to arginine deiminase modified with polyethylene glycol, to methods for treating cancer, and to methods for treating and/or inhibiting metastasis.
Malignant melanoma (stage 3) and hepatoma are fatal diseases which kill most patients within one year of diagnosis. In the United States, approximately 16,000 people die from these diseases annually. The incidence of melanoma is rapidly increasing in the United States and is even higher in other countries, such as Australia. The incidence of hepatoma, in parts of the world where hepatitis is endemic, is even greater. For example, hepatoma is one of the leading forms of cancer in Japan and Taiwan. Effective treatments for these diseases are urgently needed.
Selective deprivation of essential amino acids has been used to treat some forms of cancer. The best known example is the use of L-asparaginase to lower levels of asparagine as a treatment for acute lymphoblastic leukemia. The L-asparaginase most frequently used is isolated from E. coli. However, clinical use of this enzyme is compromised by its inherent antigenicity and short circulating half-life, as described by Y. K. Park, et al, Anticancer Res., 1:373-376 (1981). Covalent modification of E. coli L-asparaginase with polyethylene glycol reduces its antigenicity and prolongs its circulating half-life, as described, for example, by Park, Anticancer Res., supra; Y. Kamisaki et al, J. Pharmacol. Exp. Ther., 216:410-414 (1981); and Y. Kamisaki et al, Gann., 73:47-474 (1982). Although there has been a great deal of effort to identify other essential amino acid degrading enzymes for the treatment of cancer, none have been approved, primarily because deprivation of essential amino acids, by definition, results in numerous, and severe, side effects.
It has been reported that enzymes which degrade non-essential amino acids, such as arginine, may be an effective means of controlling some forms of cancer. For example, arginine deiminase (ADI) isolated from Pseudomonas pudita was described by J. B. Jones, xe2x80x9cThe Effect of Arginine Deiminase on Murine Leukemic Lymphoblasts,xe2x80x9d Ph.D. Dissertation, The University of Oklahoma, pages 1-165 (1981). Although effective in killing tumor cells in vitro, ADI isolated from P. pudita failed to exhibit efficacy in vivo because it had little enzyme activity at a neutral pH and was rapidly cleared from the circulation of experimental animals. Arginine deiminase derived from Mycoplasma arginini is described, for example, by Takaku et al, Int. J Cancer, 51:244-249 (1992), and U.S. Pat. No. 5,474,928, the disclosures of which are hereby incorporated by reference herein in their entirety. However, a problem associated with the therapeutic use of such a heterologous protein is its antigenicity. The chemical modification of arginine deiminase from Mycoplasma arginini, via a cyanuric chloride linking group, with polyethylene glycol was described by Takaku et al., Jpn. J Cancer Res., 84:1195-1200 (1993). However, the modified protein was toxic when metabolized due to the release of cyanide from the cyanuric chloride linking group.
There is a need for compositions which degrade non-essential amino acids and which do not have the problems associated with the prior art. The present invention is directed to these, as well as other, important ends.
The present invention is directed to arginine deiminase modified with polyethylene glycol. In a preferred embodiment, the arginine deiminase is modified with polyethylene glycol, having a total weight average molecular weight of about 1,000 to about 50,000, directly or through a biocompatible linking group.
Another embodiment of the invention is directed to methods of treating cancer, including, for example, sarcomas, hepatomas and melanomas. The invention is also directed to methods of treating and/or inhibiting the metastasis of tumor cells.